Battery-equipped iPhone cases are nothing new, and neither are the super-heavy duty protective options popularized by brands such as Otterbox. Yet no company has previously combined these two different concepts as completely into a single product as Mophie: Juice Pack Pro for the iPhone 4 + 4S ($130) combines military-spec case protection with a 2500mAh battery that promises a 150% additional charge. Though this is a big case, some users will find it to be an ideal way to protect and power Apple's most delicate devices.

The first thing you’ll notice about Juice Pack Pro is that it’s huge, and pictures don’t do it justice—this case is a brick. At 1.02” thick, it adds two-thirds of an inch or almost twice the thickness to an iPhone, and the weight is also substantial. It’ll still fit in average jeans pockets, but those who wear skinny jeans or other equally tight pants are out of luck. Maybe that’s why Mophie includes a detachable ratcheting belt clip with the case; the clip notably only allows your iPhone to be inserted with the back facing out.

Physical size aside, Mophie designed Juice Pack Pro strikingly well, especially considering that this is its first foray into this style of case. The core is familiar enough—a sled-like attachable plastic case connects to the iPhone through its Dock Connector port. Along the bottom you’ll find a power switch at one corner, Micro-USB port at the other, and a power indicator in the middle. Naturally a Micro-USB cable is included for recharging, and the iPhone can be charged and synced while in the case. Onto that back piece snaps a plastic frame with an integrated screen protector and rubber Home button coverage. For reasons that don’t make sense to us but don’t harm the product, Juice Pack Pro also comes with a sheet of screen film. With the top hard plastic piece in place, the iPhone is fully protected save for its volume buttons, side switch, headphone port and mic, and Sleep/Wake button.

To shield these components and add another layer of security, a rubber skin wraps around the body. It snaps into place with the hard plastic shell, and stays unless you put some real effort into removing it; you should have no worries about it accidentally becoming dislodged. Fully assembled, the case completely covers all of the ports and buttons, enabling your iPhone to become waterproof, mud proof, and drop-resistant. Flip-open covers reveal the Micro-USB port, power switch, side switch, and headphone port when they’re needed. Despite the many layers covering it, the iPhone remains totally usable. The buttons retain their tactility, and the screen works just fine through the integrated protector. Despite reports we’ve heard from some users having issues with muffled audio, the Juice Pack Pro unit we tested we didn’t exhibit any issues. A minor gripe is that removing the case is somewhat difficult—we found the best method is to pull at the headphone port cover until it separates from the plastic and then work it off.

In terms of battery performance, Juice Pack Pro is quite good but didn’t quite live up to Mophie’s promises. We did our testing on an iPhone 4 connected to a cellular network and Wi-Fi with no content playing and the screen off, and the case was able to provide 127% charge, a number that should fall a little with the iPhone 4S. While this result is actually pretty impressive compared to the average battery pack, we’d hope Mophie would market this with more accurate battery claims.

Battery-equipped cases and heavy-duty cases separately represent reasonably large segments of the iPhone accessory space, but it’s unclear just how much room for overlap there is, particularly at a $130 price—you’re effectively paying more than you might for a standalone $50 military-spec case such as Griffin’s Survivor and a comparable battery pack, but there’s no need to carry a separate battery and cable here. Even though Mophie is the only company occupying this space right now, it did a pretty good job with this hybrid design. Size aside, Juice Pack Pro is attractive, protective, provides a considerable amount of extra battery power, and comes in at only a $30 premium over Juice Pack Plus. While the appeal of this design is slightly more limited, we still consider it worthy of our general recommendation, and appreciate that Mophie has come up with something novel here. Those that need extra juice and extra protection at the same time will be quite happy with what Juice Pack Pro has to offer.

Editors' Note: iLounge only reviews products in "final" form, but many companies now change their offerings - sometimes several times - after our reviews have been published.
This iLounge article provides more information on this practice, known as revving.